A pizza is a food product of Italian origin, generally having a leavened dough base in the form of a flat disc with raised edges and having the upper face of the disc covered with a tomato paste and a meltable cheese. The pizza may have other ingredients, such as onions, mushrooms, salami slices, green peppers, etc. on top of the cheese. Some pizzas, called "Sicilian", are rectangular in shape, when viewed from above. A slice of pizza is generally called a "wedge". The pizza may be prepared by a food processor, frozen by the processor, packed in a cardboard box and sold,, at retail, in its frozen state. The user may simultaneously unfreeze and heat the pizza in a microwave oven. A microwave oven produces radio frequency energy which excites the molecules of the pizza and internally and rapidly heats it.
The user may, in some cases, remove the pizza from the cardboard container before placing the pizza in the oven. However, this may be difficult since the pizza crust may be partially frozen to the cardboard. More importantly, the crust may flake or the cheese may run over the rim of the pizza, requiring the oven to be cleaned. Since one of the major attractions of frozen pizza to the user is its convenience, the requirement to clean the microwave oven seriously detracts from that convenience.
Alternatively, the user may retain the pizza in the cardboard container and place both in the microwave oven if the container is small enough to fit in the oven, for example, if the container contains a slice of a large pizza or a small pizza. Retaining the pizza in the container during heating prevents soiling of the oven and permits the pizza to become unfrozen from the cardboard.
However, various problems may occur when the pizza is heated in its cardboard container. The pizza, especially if it has been frozen, contains a considerable amount of moisture. That moisture, under the rapid heating of the microwave oven, may turn into steam vapor. If the vapor cannot rapidly escape from the container, it may make the pizza crust moist and soggy, contrary to its desired property of crispness. In addition, if the bottom crust of the pizza is left in contact with the cardboard during heating, the crust may not be heated sufficiently or it may be heated unevenly or it may become soggy instead of becoming crisp.
U.S. Pat. No. 3,876,131 entitled "Wedge Shaped Carton", which names William Tolaas as inventor and Hoerner Corporation as assignee, shows a carton adapted to hold a frozen slice (wedge) of pizza. The carton has apertures in its bottom panel to permit the circulation of air during heating. The apertures are sealed by a strip of plastic film which is removed prior to heating. The carton bottom, during heating, is kept above the metal panel of the oven by means of the carton's side walls which extend below the level of the carton bottom.